Production of patented steel wire

ABSTRACT

A method for producing patented steel wire by depositing the wire in nonconcentric overlapping turns on a moving conveyor belt and controlling its temperature to convert its texture to ferrite and pearlite.

United States Patent Hoffmann et al.

[ Feb. 29, 1972 [541 PRODUCTION OF PATENTED STEEL WIRE [72] Inventors: Bernd l'lofimann, Dusseldorf; Georg Bollig, Buderich; Otto Dopper, Krefeld, all of Germany [73] Assignee: Schloemann Aktiengesellschaft, Dusseldorf, Germany [22] Filed: Nov. 10, 1969 [21] Appl. No.: 871,313

Related US. Application Data [62] Division of Ser. No. 635,776, May 3, 1967.

[30] Foreign Application Priority Data May 7, 1966 Germany ..38955 [52] U.S.Cl "148/156, 148/12, 148/121,

Primary ExaminerRichard 0. Dean Att0meyHolman and Stern [57] ABSTRACT A method for producing patented steel wire by depositing the wire in nonconcentric overlapping turns on a moving conveyor belt and controlling its temperature to convert its texture to ferrite and pearlit'e.

11 Claims, 6 Drawing Figures PATENTEUFEBZS I972 '3, 645 8 O5 INVENTOR5 BY a v I ATTORNEYS PRODUCTION OF PATENTED STEEL WIRE This application is a divisional application of copending application Ser. No. 635,776, filed May 3, 1967.

This invention relates to a method of and means for the production of patented steel wire from the roll heat, wherein the wire, after leaving the last roll stand, is deposited in nonconcentric overlapping turns, with a temperature above the austenite conversion temperature, upon a conveyor, and is cooled, by controlled cooling means, for at least such a length of time that the conversion of the texture of the wire into ferrite and pearlite is completed.

The steel wire produced in the usual wire-rolling mills, with a carbon content of more than'0.3 percent, must as a rule be prepared for the cold deformation process in the wire-drawing plant by appropriate heat treatment, which is generally referred to as patenting," in such a way that the wire, over its entire length, acquires a uniform and quite ductile texture. And indeed the most advantageous initial texture for the. ensuing cold deformation consist of a uniform and unitary sorbite as finely striated or laminated as possible over its entire cross section, as far as possible without segregation of ferrite on the boundaries of the grains, and with the largest possible granules of sorbite. This texture is aimed at by the patenting process, in which the wire is heated to temperatures above the A 3 temperature, mostly between 850 and l,l C., and is maintained for some time usually from 1 to 2 minutes, in the austenitic range. Thereupon a rapid cooling is effected by immersing the wire in a lead bath or a salt bath of about 500 to 550 C., or by means of an air blast, the austenitic texture being converted into a fine pearlitic to sorbitic texture.

In order to obviate the expenditure for this patenting plant, attempts have already for a long time been made, by controlled cooling in conjunction with the rolling process, to produce a steel wire with improved drawing properties. Thus wire-rod rolling mills are already known, in which the wire, after leaving the last roll stand, is precooled in a cooling water section, and thereupon deposited in coils, or else in nonconcentric overlapping turns, upon a conveying means, and further cooled, by controlled air cooling, at least until the conversion of the texture of the wire into ferrite and pearlite is completed.

In this way it was indeed possible greatly to improve the drawing properties of the steel wire, but they did not attain those of an air-patented wire, and did not by far attain those of a lead-patented or of a salt-patented wire. This is connected with the fact that in the rolling process the texture of the wire acquires a very fine-grained structure, and, owing to the ensuing abrupt cooling, the austenitic grains, in the time up to reaching the conversion temperature, cannot grow up again to the size which they attain with air or lead patenting, owing to being kept longer at the austenitising temperature.

From the patent literature it is further known to deposit the wire upon the conveyor with a temperature close to but above the conversion temperature, and furthermore also to control the size of the grains by varying the speed of cooling before the allotropic conversion. These measures however are not suitable for a growth of grain in the texture of the wire, because the temperature of the wire, on account of the speed of cooling, of about 6 to 7 C. per second, conditioned by the thermal radiation at these temperatures, has already fallen below the conversion temperature after a few seconds. Furthermore a growth of grains is here not contemplated at all, since a fine-grained texture is frequently held to be desirable.

Now it is the object of this invention to improve the drawing properties of a rolled steel wire with more than 0.3 percent carbon by increasing the size of grain during the cooling operation, and also to counteract the scaling of the wire.

According to the method of this invention, in a process of the kind hereinbefore described, this is attained by the feature that the wire, after being deposited upon the conveyor, is maintained above the austenite conversion temperature until the texture of the wire has reached a size of grain below or equal to according to the ASTM standard.

In connection with the holding time above the austenite conversion temperature, the wire is cooled in such a way that the desired texture formation occurs. The cooling may be differently effected, for instance in air, advantageously also in lead or salt baths, or in the vortex bed, to be described below.

This method has, however, as will be gathered from FIG. and FIG. 3 of the accompanying drawings, also the further advantage that the ranges of conversion in the ZTU diagram, with increasing size of grain, are displaced towards longer times, and accordingly are carried out at lower temperatures. This however involves at the same time the formation of a more finely laminated j-pearlitic to sorbitic texture, and furthermore less segregation of ferrite on the boundaries of the grains.

With respect to the great scaling tendency of steel at austenite temperatures, and the descaling expenditure associated therewith, in the wire-drawing plant it is advantageous if the holding of the wire temperature above the conversion temperature is effected in a nonoxidizing atmosphere. This constitutes a further feature of the invention Furthermore, for a shortening of the holding time above the conversion temperature, it is also advantageous if the wire, according to an additional feature of the invention, is deposited upon the conveyor at a temperature of from 50 to C. above the conversion temperature.

In the case of qualities of steel having admixtures of undissolved constituents embedded in them, such for example as carbides, nitrides or oxides, it will even additionally be necessary that the wireshould be protected against cooling when being guided on its way to the laying'device. This is likewise a feature of the invention; for these inclusions have the property of hindering the growth of the grains, so that the wire then has to be deposited upon the conveyor at as high a temperature as possible, in order that the austenitic grains may be able to attain the desired size in the grain-growing tract provided.

A further feature of the invention consists in the fact that the temperature of the turns of wire, in the range above the conversion temperature, is influenced in the direction of being maintained constant. As constant a temperature as possible can according to the invention on the one hand be attained by counteracting a loss'of heat of the turns of wire by thermal insulation. On the other hand, according to the invention, a loss of heat of the turns of wire can be counteracted by supplying heat.

For carrying out this method, apparatus according to the invention is to ensure that the lying time of the turns of wire upon the conveyor belt before the cooling tract is adjustable in such a way that in dependence upon thecross section of the wire, the temperature on leaving the rolls, and the quality of the wire, the most advantageous temperature of the wire in each instance can be selected at its entry into the cooling tract.

For the solution of the problem set forth, by means of apparatus for the production of patented steel wire from the roll heat, in the case of which a wire reel with a wire-feeding device arranged before it, is followed by a conveyor belt for the deposition of the steel wire in nonconcentric overlapping turns and for the transport of the latter to a coil-collecting station, a texture-converting cooling tract being provided in the rear region of the conveyor belt, it is proposed according to the invention that the distance between the rotating tube reel and the beginning of the cooling tract should be adjustable, and for this purpose the rotating tube reel is movably arranged over the front region of the conveyor belt about parallel to the direction of conveyance to a point in front of the cooling tract, and the wire-feeding device preceding the rotating tube reel is adjustable to the .change in the feeding length connected with the procedure of the rotating tube reel.

cooling tract, and therefore in a change in the temperature of 5 the rolled stock upon its entry into the cooling tract. The apparatus according to the invention renders it possible, by simple means, to adjust reliably the most advantageous temperature of the wire for the most varied qualities and dimensions at its entry into the cooling tract.

The constructional expenditure connected with the mobility of the rotating tube reel is simplified, according to a further feature of the invention, by the fact that the rotating tube reel is provided with a rotating tube revolving about a horizontal axis, which is followed by a device for tilting the turns of wire over, the axis of the rotating tube being arranged in substantially rectilinear alignment with the direction of rolling. This has the advantage, as compared with the rotating tube reel usually employed, with a rotating tube revolving about a vertical axis, that the distance between the last roll stand and the rotating tube reel can be considerably shortened by the fact that the parabolic wire-looping adapted to the speed of the wire, or a guiding or reversing driver as a substitute for this above the rotating tube reel, can be dispensed with. Moreover the changing of the feeding length in the case of the wire-feeding device is by this means considerably facilitated.

In order to obviate the straightening or adjusting of the guiding tubes connected with the reconstruction of the wirefeeding device, and to shorten the time occupied by the reconstruction, the wire-feeding device, according to an additional feature of the invention, consists of individual guiding tubes secured to rockable arms, these guiding tubes being so arranged as to be rockable in and out, individually or in groups, transversely to the direction of feed of the wire. In this case it is furthermore advantageous, according to the invention, that to the rockable arms, holding positions are allocated for the inwardly and outwardly rocked positions of the guiding tubes.

An advantageous development of the invention consists moreover in the feature that above the conveyor belt, between the rotating tube reel and the cooling tract, a thermally insulating roofing tunnel, adjustable to the particular distance between these, and wholly or partly covering the conveyor belt between the rotating tube reel and the cooling tract, is removably arranged, and can be filled with neutral gas.

By means of the rotating tube reel, variable in its distance from the cooling tract, in combination with the thermally insulating roofing tunnel, the grain growth and the scale formation, as well as the entry temperature of the wire into the cooling medium, admit of being influenced in a manner which is advantageous for the drawing of the wire.

The grain growth, in such a manner that in cases in which the most advantageous entry temperature of the wire into the cooling medium would require a shorter lying time upon the conveyor belt than is desirable for the grain growth, the cooling upon the conveyor belt by the thermally insulating roofing tunnel is so far slackened that the distance from the rotating tube reel to the cooling tract can be selected sufficiently long to obtain, besides the desired entry temperature of the wire into the cooling medium, also a sufficiently long lying time for the grain growth upon the conveyor belt.

In order to obviate an undesirably stout formation of scale, the roofing tunnel may be filled with a neutral gas.

Hence, with the apparatus according to the invention, the conditions most advantageous for any quality of wire, as regards patenting texture, size of grain and formation of scale, can be adjusted.

The invention will now be further described with reference to the accompanying drawings, in which:

FIG. 1 shows a wire-treating plant, in conjunction with a rolling mill, in a greatly simplified representation;

FIG. 2 shows an isothermal ZTU diagram for steel of medium carbon content and fine-grained texture, with a diagrammatic representation of different methods of cooling;

FIG. 3 shows an isothermal ZTU diagram for steel with the same carbon content and of coarse-grained texture, with a diagrammatic representation of the method of cooling according to the invention in comparison with the other method;

FIG. 4 shows a side view of the movable rotating tube reel according to the invention, in the front end position, with,the wire-feeding device swung out;

FIG. 5 shows the rotating tube reel in its rear end position, with the wire-feeding device swung in; and I FIG. 6 shows a section through the wire-feeding devicein a direction towards the rotating tube reel. 3

In FIG. 1, the rolled wire, after leaving the last roll stand 1, passes through a wire guide 2, which, according to the quality of the steel, serves also as a cooling water tract for the rolled wire, and is then deposited, by a laying device 3, in connection with a tripping edge 4, in nonconcentric overlapping turns, upon a conveyor 5, with a temperature above the austenite conversion temperature, and is supplied by the latter to a coilcollecting means 8.

Under these circumstances the turns of wire, after being deposited upon the conveying device 5, first traverse a graingrowth stretch 6, in which the wire temperature, either by thermal insulation or by supplying heat, is kept as constant as possible, the atmosphere surrounding the turns of wire being nonoxidizing. The supply of heat may be effected either by electric heating and by gas heating, the gas heating presenting the advantage of producing in a simple manner, by burning without an excess of air, a nonoxidizing atmosphere, and thus counteracting excessive scaling of the wire.

In conjunction with the grain-growth tract 6, the turns of wire pass through a cooling tract 7, in which, by a controlled air-cooling means not shown, the conversion of the texture of the wire from austenite to ferrite and pearlite is carried out in a known manner.

In FIG. 2, the curve a represents the progress of the cooling in lead patenting, whilst the curve 11 represents in a simplified form the progress of the cooling of a steel wire, which, after leaving the last roll stand, and after passing through a coolingwater tract, is deposited by a laying device upon a conveying device. Even though, in the case of the curve b, it is not a question of an isothermal conversion, this diagrammatic representation of the different methods of cooling furnishes the possibility of a qualitative comparison.

With the lead patenting process, the steel wire, by immersion in a lead bath with a temperature of about 500 to 550 C., is very rapidly cooled down from its austenitising temperature, and is then maintained, up to the end of conversion, at an approximately constant temperature. The cooling curve crosses the conversion lines as precisely as possible at the pearlite peak above the intermediate stage range and below the ferrite segregation, so that the wire acquires a purely sorbitic texture.

The speed of cooling of the method according to the curve b is however so controlled that the cooling curve b crosses the inner line in the ZTU diagram, that is to say, the line of the completed pearlite conversion, as nearly as possible in the neighborhood of the peak. Thus ferrite is separated out first, and then pearlite, which, with time, always becomes more finely laminated, and, at the end of the conversion, also contains portions of sorbite.

Whilst in FIG. 2 the conversion lines for a fine-grained steel with a medium carbon content are marked, the conversion lines in FIG. 3 are those of a coarse-grained steel with the same carbon content, wherein the beginning and the end of the conversion in the pearlite range are shifted to longer times. Likewise the field of the formation of ferrite by coarse-grained initial texture is diminished, so that less ferrite is segregated on the grain boundaries. The curve 0, according to the cooling method of this invention, crosses the inner conversion line at the same place as the curve b. Since the inner conversion line, however, is displaced to longer times, this method has, according to the curve 0 as compared with that of the curve b, a slower cooling speed, that is to say, the curve c crosses the conversion range more flatly, and approaches the curve a, so that with the method according to the invention the pearlite turns out to be more finely laminated than with the cooling of a fine-grained wire texture.

The rectilinear representation of the cooling curves b and c is not quite correct, in so far as the speed of cooling with a falling temperature, owing to the decreasing temperature difference from the cooling air, is likewise smaller, and furthermore, with the allotropic conversion of austenite into ferrite, heat is liberated, and moreover in the ZTU diagram, time is generally marked on a logarithmic scale. Since however the curves b and c have been represented with the same defect, the qualitative comparison of the two cooling curves is not upset thereby. A comparison of the cooling curves in the complicated continuous ZTU diagram would yield exactly the same result.

In FIG. 4 the rolled wire, after leaving the last roll stand 1, likewise passes through a wire-feeding device 2, and is then deposited, by a rotating tube reel 3, with a rotary tube 14 revolving about a horizontal axis, in conjunction with a tripping edge 4 which lays the turns of wire over, in nonconcentric overlapping turns upon a conveyor belt 5, and by the latter, after passing through a cooling tract 7 that serves for the conversion of texture, is supplied to a coil-collecting appliance 8. In the wire-feeding device 2 the wire may be slightly precooled by means of water, which will be particularly advantageous in the case of wire of thick cross sections, in order not to have to build the precooling tract on the conveyor belt particularly long with respect to those wire cross sections. Care is however to be taken that the water cooling is put in only to such an extent as not to impair the uniform formation of the wire texture, having regard to the disadvantages, described in the introduction, of a water cooling that is too abrupt. Only iron wires (qualities of low carbon content, below about 0.3 percent) may be cooled in the wire-feeding device 2, by a specially strong water cooling, down to about 600 C. or lower, in order as far as possible to prevent any formation of scale, and, it may be, to obtain any unavoidable scaling as waste, the wire then not being guided through the cooling medium in the cooling tract 7. The cooling tract 7 may be constructed in a known manner as a lead, salt or vortexsheet bath, through which the conveyor belt, with the turns of wire lying upon it, is guided on rails.

The vortex-sheet bath which is preferably employed in the present invention is produced in a container in such a way that gas, supplied through tubes not shown, passes through the pores of a gas-permeable plate, likewise not shown, and in so doing whirls up or pseudoliquefies a layer, resting upon the plate, of rather small and very small particles of the cooling medium. Since the speed of cooling of the turns of wire depends not only upon the thermal conductivity of the cooling medium but also upon its temperature differences from the cooling medium, the effectiveness of the vortex-sheet bath can be further increased by adjusting the temperature in its front portion considerably lower than in the middle and in its rear portion, where it should amount to about 500 to 600 C., according to the quality of the wire. For this purpose the space underneath the gas-permeable plate is divided into individual chambers, into which the gas is supplied at different temperatures, increasing from the beginning of the vortex-sheet bath to the end of it. If necessary, nonoxidizing gas may here be employed, in order to reduce the formation of scale.

The apparatus may in a simple manner be so designed that wires of qualities which do not need to pass through the cooling tract are passed above the latter, for instance by raising the rails that guide the conveyor belt. This is particularly simple to accomplish with a vortex-sheet bath, in which the depth of the bath sinks considerably when the gas that whirls up the cooling medium is switched off.

The rotating tube reel 3 is so arranged as to be movable on rails 9 over the front region of the conveyor belt 5 substantially parallel to the direction of conveyance as far as a point in front of the cooling tract 7, so that the distance between the rotating tube reel 3 and the beginning of the cooling tract 7, or in other words the lying time of the turns of wire upon the conveyor belt 5, up to the entry into the cooling tract 7, can be adapted to comply with particular requirements.

In the section shown in FIG. 6 are illustrated guiding tubes 10, which are secured to rockable arms 11, and are so arranged as to be rockable in and out, individually or in groups, transversely to the direction of feed of the wire. To the arms 11 are allocated in each case a holding station 12 for the rocked-in position and a holding station 13 for the rocked-out position of the guiding tubes 10. By this means, during the travel of the rotating tube reel 3, the wire-feeding device 2 can be quickly and simply adjusted to the altered feeding length. Over the conveyor belt 5 there may be set, between the rotating tube reel 3 and the cooling tract, a heat-insulating roofing tunnel 6, which is subdivided into equal individual lengths to correspond to the length of the guiding tubes 10, so that the roofing tunnel 6 can be adjusted to the existing distance between the rotating tube reel 3 and the cooling tract. The roofing tunnel 6 is in the first place for the purpose of counteracting, with definite qualities of steel wire, a too rapid cooling of the turns of wire, by thermal insulation, and of keeping the temperature of the wire, over the entire length of the roofing tunnel 6, sufficiently high above the conversion temperature to promote the growth of the grains. Moreover the roofing tunnel may be filled with neutral gas, in order to obviate the formation of scale in the case of qualities in which, on any of the grounds described, a lying time before the cooling in the cooling tract is desirable.

We claim:

1. A method for the production of patented steel wire from the roll heat, comprising the steps of: depositing the wire, as it leaves the last roll stand, in nonconcentric overlapping turns upon a moving conveying surface at a temperature above the austenite conversion temperature, and maintaining the temperature of the wire on the conveying surface above the austenite conversion temperature until it attains a size of grain not greater than 5 on the ASTM scale, and then subjecting the wire to controlled cooling until its texture is completely converted to ferrite and pearlite.

2. A method for the production of patented steel wire as claimed in claim 1, comprising the further step of cooling the wire in air after the said size of grain has been reached.

3. A method for the production of air-patented steel wire as claimed in claim 2, the maintenance of the temperature of the wire above the austenite conversion temperature being effected in a nonoxidizing atmosphere.

4. A method for the production of air-patented steel wire as claimed in claim 2, the wire being deposited upon the conveying surface at a temperature of from 50 to C. above the austenite conversion temperature.

5. A method for the production of air-patented steel wire as claimed in claim 2, comprising the step of protecting the wire from loss of heat on its way to the depositing means.

6. A method for the production of air-patented steel wire as claimed in claim 2, comprising the step of influencing the temperature of the turns of wire, in the range above the austenite conversion temperature, in the direction of keeping it constant.

7. A method for the production of air-patented steel wire as claimed in claim 2, comprising the step of counteracting any loss of heat from the turns of wire by thermally insulating them.

8. A method for the production of air-patented steel wire as claimed in claim 2, comprising the step of counteracting any loss of heat from the turns of wire by supplying heat to them.

9. A method for the production of patented steel wire as claimed in claim 1, comprising the steps of maintaining the temperature of the wire above the austenite conversion temperature in a nonoxidizing atmosphere, and depositing it upon the conveying surface at a temperature of from 50 to 100 C. above the austenite conversion temperature.

10. A method for the production of patented steel wire as claimed in claim 1, comprising the step of protecting the wire from loss of heat on its way to the depositing means.

11. A method for the production of patented steel wire as claimed in claim 1, comprising the step of supplying to the turns of wire above the austenite conversion temperature a sufficient amount of heat to counteract their loss of heat. 

2. A method for the production of patented steel wire as claimed in claim 1, comprising the further step of cooling the wire in air after the said size of grain has been reached.
 3. A method for the production of air-patented steel wire as claimed in claim 2, the maintenance of the temperature of the wire above the austenite conversion temperature being effected in a nonoxidizing atmosphere.
 4. A method for the production of air-patented steel wire as claimed in claim 2, the wire being deposited upon the conveying surface at a temperature of from 50* to 100* C. above the austenite conversion temperature.
 5. A method for the production of air-patented steel wire as claimed in claim 2, comprising the step of protecting the wire from loss of heat on its way to the depositing means.
 6. A method for the production of air-patented steel wire as claimed in claim 2, comprising the step of influencing the temperature of the turns of wire, in the range above the austenite conversion temperature, in the direction of keeping it constant.
 7. A method for the production of air-patented steel wire as claimed in claim 2, comprising the step of counteracting any loss of heat from the turns of wire by thermally insulating them.
 8. A method for the production of air-patented steel wire as claimed in claim 2, comprising the step of counteracting any loss of heat from the turns of wire by supplying heat to them.
 9. A method for the production of patented steel wire as claimed in claim 1, comprising the steps of maintaining the temperature of the wire above the austenite conversion temperature in a nonoxidizing atmosphere, and depositing it upon the conveying surface at a temperature of from 50* to 100* C. above the austenite conversion temperature.
 10. A method for the production of patented steel wire as claimed in claim 1, comprising the step of protecting the wire from loss of heat on its way to the depositing means.
 11. A method for the production of patented steel wire as claimed in claim 1, comprising the step of supplying to the turns of wire above the austenite conversion temperature a sufficient amount of heat to counteract their loss of heat. 